[turbofan] Introduce explicit loop exits markers.

src/compiler/control-builders.cc

Index: src/compiler/control-builders.cc
diff --git a/src/compiler/control-builders.cc b/src/compiler/control-builders.cc
index 6905ef589ff56c11b18ac6717969d726aee56577..d6b8b4050b84f5aad493cbc55a357dbfd4c5a3af 100644
--- a/src/compiler/control-builders.cc
+++ b/src/compiler/control-builders.cc
@@ -36,6 +36,7 @@ void LoopBuilder::BeginLoop(BitVector* assigned, bool is_osr) {
   loop_environment_ = environment()->CopyForLoop(assigned, is_osr);
   continue_environment_ = environment()->CopyAsUnreachable();
   break_environment_ = environment()->CopyAsUnreachable();
+  assigned_ = assigned;
 }
 
 
@@ -60,6 +61,7 @@ void LoopBuilder::EndBody() {
 void LoopBuilder::EndLoop() {
   loop_environment_->Merge(environment());
   set_environment(break_environment_);
+  ExitLoop();
 }
 
 
@@ -82,6 +84,16 @@ void LoopBuilder::BreakWhen(Node* condition) {
   control_if.End();
 }
 
+void LoopBuilder::ExitLoop(Node** extra_value_to_rename) {
+  if (extra_value_to_rename) {
+    environment()->Push(*extra_value_to_rename);
+  }
+  environment()->PrepareForLoopExit(loop_environment_->GetControlDependency(),
+                                    assigned_);
+  if (extra_value_to_rename) {
+    environment()->Pop();
+  }
+}
 
 void SwitchBuilder::BeginSwitch() {
   body_environment_ = environment()->CopyAsUnreachable();